/Engine/Plugins/Runtime/GameplayAbilities/Source/GameplayAbilities/Public/GameplayAbilitySet.h
E.g., "Ability1" is the command string that is bound to AbilitySystemComponent::ActivateAbility(1). The Meta data onlysuggeststhat you are binding "Ability1" to LMB by default in your projects DefaultInput.ini.
namespace EGameplayAbilityInputBinds { enum Type { Ability1, Ability2, Ability3, Ability4, Ability5, Ability6, Ability7, Ability8, Ability9, } }